This invention relates to satellite communications and more particularly to a satellite-based communications network and a satellite payload architecture for use in the extremely-high-frequency (EHF) bands.
In the emerging EHF bands of 20-60 GHz for use in satellite communications, use of traditional bent-pipe repeaters and single-uplink/downlink beams is no longer a viable architecture for systems that need to support the emerging information distribution and interactive broadcasting services targeted to mass markets. For widespread appeal, such systems must allow easy and low-cost access to the satellites by all information content providers, scattered throughout the coverage area, on a bandwidth-on-demand, as-needed basis.
With traditional payload designs, a satellite with a single uplink beam over a relatively large service area has a much lower gain/temperature figure of merit than that of a spot-beam design. For example, a single beam covering the 48 contiguous U.S. states has an edge-of-coverage gain/temperature value of about 0 dB/K. The same area can easily be covered by 100 0.5-degree spot beams each with an edge-of-beam gain/temperature of about 17 dB/K. This means that for uplinking the same information rate to the satellite one requires approximately 17 dB (a factor of 50 times) more radiated power with the single-beam design than with spot-beam designs. Provision of this additional amount of radiated power in the 20-60 GHz frequency bands, coupled with the much higher link margins needed for rain attenuation compared to those required for the lower frequency bands, makes the cost of uplinking too expensive, and operationally not desirable, to many would-be service providers.
A further requirement is the need to downlink wide-band, high-data-rate time-division-multiplexed (TDM) carriers. This allows for use of lowest-cost receive terminals, as well as, dynamic multiplexing of data packets from multiple services at the highest transmission efficiencies. To achieve these benefits with conventional bent-pipe satellite payloads, one has to back-haul the service/program contents from hundreds or thousands of distribution sites to a few designated central uplink sites. This is operationally inconvenient and expensive, and it is not conducive to the development of low-cost information distribution and broadcasting service markets.
The present invention overcomes the drawbacks of prior art systems through the provision of a new system and satellite payload architecture in support of the emerging interactive information distribution and broadcasting services in the new extremely-high-frequency bands (20-60 GHz). The system allows multiple service-program providers to access the system on a bandwidth-on-demand and on an as-needed basis. Furthermore, the service-program providers can directly transmit to the satellite from their premises through small, low-power, low-cost terminals, to provide a plurality of one-way and interactive information distribution services, including video, to small low-cost user/subscriber terminals on a controlled basis.
The present invention has many advantages over bent-pipe or back-hauled payload designs. The present invention includes such features as: (1) low-cost, individual or xe2x80x9cpersonalxe2x80x9d broadcasting terminals, (2) concurrent access to multiple program.(information) channels by a single end-user terminal, (3) return transmission capability for interactive applications, (4) direct transmissions to the satellite by all service-program providers on a bandwidth-on-demand and as-needed basis, (5) elimination of terrestrial backhaul transmission and very expensive uplink facilities at centralized hubs, (6) maximizing satellite transmission efficiency and system throughput, (7) providing maximum flexibility in allocation of uplink access capacity to all parts of the service area, and (8) support of single-hop mesh connectivity for special supplementary services among user terminals.
The new payload employs high-gain spot beams for low-cost uplinking, on-board signal regeneration and processing for transmission efficiency and multiplexing, and full-area broadcast downlink beams essential for wide-area coverage. User/subscriber terminals equipped with transmit capability can directly interact with the service-program providers in support of the emerging interactive Internet and multimedia applications and services. Multiplexing of large amounts of information onto wide-band downlink broadcast TDM carriers enables receive terminals to have concurrent access to multiple information service programs or channels.
Use of on-board data regeneration, processing and multiplexing allows every service-content provider to transmit at its own individual data-rate needs, which usually is much lower than the required TDM rates used for downlinking. The multiplexing function of the payload groups the received information data-packets into one or more TDM streams. The TDM streams are transmitted via a single broadcast beam to achieve optimum networking features, service delivery, and bandwidth utilization efficiency. Use of on-board signal processing further provides for maximum flexibility in access to the broadcast capacity from any location in the service area, thus achieving a substantial improvement in system utilization over the bent-pipe payloads. Use of high-gain uplink spot beams also provides for low-cost return transmissions by the small user terminals throughout the satellite coverage area. Such return transmission capability allows the system to support all types of emerging interactive multimedia and broadcasting services that otherwise would require the use of separate terrestrial return communication channels.
While the proposed system can be implemented with many different transmission technologies, one embodiment, particularly suited for downlink transmissions, is to make the system.as compatible with the emerging MPEG-DVB broadcast standards as possible. This is due to the fact that the MPEG-DVB standards are being adopted worldwide by most of the current generation of direct broadcast satellite systems for video and data distribution services.
Conventional ground-based systems employ the MPEG-2 standard for source encoding and multiplexing, whereby constituent digitized/compressed components of each program or service, such as video, audio and any associated data, are either combined into individual program transport streams or multiplexed with components of several other programs into one composite high-rate TDM transport stream, one per satellite transponder, for final distribution to subscriber terminals. As part of the transport-multiplexing stage, additional program specific information is also added to the transport stream in order for the subscriber terminals to properly access each transport stream and recover the authorized program-data streams. These systems, however, use traditional bent-pipe satellites which require the service-programs to be backhauled to a few ground-based uplink sites for MPEG-DVB processing and multiplexing. The proposed compatibility with MPEG-DVB broadcast standards under this invention should reduce the overall system development cost and result in a much lower cost for the end-user subscriber terminals.
In addition to its general use as an interactive information distribution network, the proposed system architecture can easily be adapted and employed for local-TV program distribution. In such an embodiment, each broadcaster can uplink its programming directly from its premises, through a low-cost terminal, instead of back-hauling the information to a centralized broadcast center as in present systems. When used for such services, because of the local nature of distribution, the satellite payload can be equipped with multiple xe2x80x9clocalxe2x80x9d or xe2x80x9cregionalxe2x80x9d downlink beams for maximum power efficiencies.
The disclosed system architecture also supports direct single-hop connections among low-cost subscriber terminals for low-volume point-to-point communications in support of supplementary services associated with the primary services.